CHAPTER XYI. 



CONCLUDING REMARKS. 



2.16.01. In review of the western border of the country, we 

 note the elevated plateau rising from the Mississippi to the Rocky 

 Mountain range, which consists of various ranges of general north 

 and south or northwest and southeast trend, with broad valleys 

 between. Next comes the Colorado Plateau, and then the Wa- 

 satch Mountains and the Great Basin, with its various subordinate 

 north and south ranges. *These are succeeded by the Sierra Ne- 

 vada, and the great valley of California, the Coast range, and 

 finally the Pacific Ocean. 



From the Archaean to the close of the Carboniferous there 

 were granite islands around which active sedimentation proceeded. 

 At the close of the Carboniferous the elevation of the Wasatch 

 and the region of eastern Nevada occurred. At the close of the 

 Jurassic the elevation of the Sierra Nevada took place. The chief 

 upheaval of the Rocky Mountain system came at the close of the 

 Cretaceous and that of the Coast range at the close of the Miocene 

 Tertiary. Smaller and less important oscillations have occurred 

 before and since. Each elevation was accompanied by foldings, 

 faultings, and extensive outpourings of eruptive rocks. The re- 

 sultant fractures and the solfataric action, occasioned by the 

 dying volcanic activity, constitute the primary cause of the for- 

 mation of the ore deposits, which in some cases lie in ranges along 

 the lines of faulting or of disturbances, and in others are irreg- 

 ularly scattered. We can recognize the Coast range belt with 

 mercury and chromium ; the California gold belt in the western 

 Sierras; the silver belt of Utah on the western flank of the Wa- 

 satch ; a belt in Arizona from southeast to northwest, along the 

 contact between Paleozoic limestone, mostly Carboniferous, and 

 the Archaean ; and the great stretch of lead-silver mines in the 

 Carboniferous limestones of Colorado. The other areas are scat- 



